1 / 21

Contents

Quality-evaluation of Cesium Iodide photocathodes for the ALICE/High Momentum Particle Identification detector by means of a VUV-Scanner system Herbert Hoedlmoser on behalf of the ALICE/HMPID collaboration 5 th International Workshop on Ring Imaging Cherenkov Counters RICH 2004. Contents.

conway
Download Presentation

Contents

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Quality-evaluation of Cesium Iodide photocathodes for the ALICE/High Momentum Particle Identification detector by means of a VUV-Scanner system Herbert Hoedlmoser on behalf of the ALICE/HMPID collaboration 5th International Workshop on Ring Imaging Cherenkov CountersRICH 2004

  2. Contents • CsI RICH concept:detection of Cherenkov light with CsI photo-cathodes (PCs) • CsI photocathodes:substrate & CsI deposition facility • In-situ quality control by the VUV Scanner:2D scan of photocurrent on PCs • Series production of PCs:status and comparison of measurements in the scanner with test-beam results • Studies of CsI properties: - post deposition heat enhancement - ageing due to exposure to humid air - recovery effect due to annealing • Ageing of CsI PCsdue to ion bombardement inside the detector • Conclusions and outlook RICH 2004 Herbert Hoedlmoser – CERN

  3. The ALICE/HMPID Detector • Concept: proximity focussing CsI RICH • liquid C6F14 radiator • MWPC • cathode pads coated with CsI • 3840 pads per PC with individual analogue readout • 7 modules: total area 11 m2largest application so far • 42 PCs (64 cm x 40 cm) in total (6 per module) RICH 2004 Herbert Hoedlmoser – CERN

  4. 2 Photo Cathode pcb’s 40 cm 60 cm Alu frame grounding plate (double sided Cu pcb) Substrate for the CsI photocathode (PC) double layer Cu clad PCB coated with Ni, Au RICH 2004 Herbert Hoedlmoser – CERN

  5. pcb substrate protective box CERN CsI PC deposition plant • Evaporation of pre-melted CsI powder from 4 sources by resistive heating inside a 2000 l vacuum chamber • Deposition of 300 nm CsI controlled with thickness monitors • Labview online monitoring & control • Protection box to close the PC under Argon atmosphere after deposition and quality control Thickness monitor PC 4 CsI sources + shutters Remote controlled enclosure box RICH 2004 Herbert Hoedlmoser – CERN

  6. D2 light source PC current reading +100V PM Translation stage Reference CsI PM Quality control: VUV-Scanner Quality control: VUV scanner Measurement of the photocurrent on the cathode: 2D scan of the photo-current across the PC surface with a beam of UV light from a D2 source diameter of UV spot: 16mmphoto-e- extracted from PC by anode biasreference measurement on a photomultiplier by means of rotative mirror RICH 2004 Herbert Hoedlmoser – CERN

  7. X-motion Y-motion VUV-Scanner: 2D scan of the PCs X-motion 2D movement of the UV-beam on the PC PC moves in x-direction, optical system in y-direction, movement controlled by Labview RICH 2004 Herbert Hoedlmoser – CERN

  8. Normalized current and measurement uncertainties normalization of the photocurrent from the PCto the reference on the PM repeated measurements of asingle position on the PC:  = 2 % RICH 2004 Herbert Hoedlmoser – CERN

  9. Series production of CsI PCs For each PC: overview scan of 280 points on the PC Example PC 46: Mean value: <Inorm> = 3.71 min-max variation 6% other PCs: inhomogeneities up to 10% - 12% min – max TB results (with single photon counting) confirm these inhomogeneities. Mean values used to compare PCs RICH 2004 Herbert Hoedlmoser – CERN

  10. Series production of CsI PCs 17 PCs produced since May 2004variation of final level of mean photocurrent: 33 % max-min RICH 2004 Herbert Hoedlmoser – CERN

  11. Possible reason for discrepancy:slow long term increase in QEbetween scanner and TB measurement  re-scan e.g. PC 55 in the scanner Comparison of test beam and scanner results Number of resolved clustersper track comparedwith mean photocurrent at the position of the Cherenkov ring 15 clustersminimum requirement RICH 2004 Herbert Hoedlmoser – CERN

  12. Study of CsI PC properties with a test PC • Test PC to study CsI properties: • Post deposition heat enhancement • Ageing due to exposure to humid air • Recovery effect due to annealing RICH 2004 Herbert Hoedlmoser – CERN

  13. Heat enhancement, exposure, recovery • Example for a CsI deposition on the test-PC: • Evaporation at room temperature (23 °C) increase in temperature to trigger enhancement effect • Continuous scan of the photocurrent on the PC during enhancement phase • Plot of an average current from 50 points in time to visualize enhancement and recovery effects RICH 2004 Herbert Hoedlmoser – CERN

  14. Heat enhancement, exposure, recovery RICH 2004 Herbert Hoedlmoser – CERN

  15. Heat enhancement in the series production Conclusion: difference between good and bad PCs largely due to different efficiency of the heat enhancement! RICH 2004 Herbert Hoedlmoser – CERN

  16. CsI CsI - - PC PC irradiation spot irradiation spot Sr90 Sr90 C6F14 Test beam Sr90 Sr90 annular annular Cherenkov Cherenkov fiducial fiducial zone zone Ageing due to ion bombardement • Study of the ageing effects due to radiation causing bombardement of the PC with avalanche ions • Irradiation of the PC inside a detector with Sr 90 sources • Irradiation of 3 positions located on a Cherenkov ring for subsequent test beam analyses • Only 8 wires across the irradiated positions on HV RICH 2004 Herbert Hoedlmoser – CERN

  17. Decreased photo-current in aged zones Results obtained with the VUV-scanner for 3 irradiation with different doses of accumulated charge anode wires • Profile of the irradiated zones: • narrow, sharp across the wires wide along the wires •  effect caused by avalanche ions RICH 2004 Herbert Hoedlmoser – CERN

  18. Time development: continued degradation without further irradiation First tests: irradiation with very high doses and doserates!For which doses / doserates does this effect start? RICH 2004 Herbert Hoedlmoser – CERN

  19. Dose-effect relation from 3 different irradiated zones Different doses on 3 irradiated positions Dose-response relation for 49 days and 129 days after irradiation (time effect taken into account by interpolation) Pos 2 Pos 1 Pos 3 expected dose for 10 y ALICE (0.5 mC/cm2) RICH 2004 Herbert Hoedlmoser – CERN

  20. Dose-effect relation from dose profile inside a single zone Dose variation within position 1 2nd method to calculate a dose-effect relation: use the variation of the dose within one irradiated spot (charge profile) and compare to the measured profile of the decrease measurement 129 days after irradiation on position 1 Dose-effect relation from dose profile insidea single zone Dose-effect relation from irradiationsin 3 zones with different dose  good agreement RICH 2004 Herbert Hoedlmoser – CERN

  21. Conclusions & outlook • Series Production of PCs • Continuation of the series production of PCs after some difficulties with the setup after repairs of turbo pump. - Re-measure one of the PCs in the scanner, for which TB and scanner did not agree • Ageing Test • - New irradiations with lower doses and lower dose-rates - Attempt to understand the process behind the degradation (deposition of a layer of ions on the PC?) - Try a different analysis (small sample, electron microscope?) RICH 2004 Herbert Hoedlmoser – CERN

More Related